Preheat oven to 400°F (200°C). Line a large, rimmed baking sheet with parchment paper.
In a large bowl, combine potatoes, broccoli, and red bell pepper. Drizzle with olive oil, season with salt and pepper, and toss to coat. Spread on one side of the baking sheet.
Pat chicken dry and slice thick breasts horizontally if needed. Place chicken on the other side of the sheet pan, spacing away from vegetables.
In a small microwave-safe bowl, melt the butter. Stir in garlic, Italian seasoning, thyme, and paprika until fragrant.
Drizzle half the garlic butter over chicken and brush the rest over vegetables.
Roast in the oven for 15 minutes.
Remove, flip chicken, and toss vegetables. Return to oven and roast for 10-15 minutes more, until chicken reaches 165°F internally and vegetables are golden.
Garnish with lemon juice and fresh parsley. Serve hot.